From dbb51fd1d0133b503871c30cc1a94f1d3d170348 Mon Sep 17 00:00:00 2001
From: Michael Zhang <mail@mzhang.io>
Date: Sun, 17 Jul 2022 22:26:11 -0500
Subject: [PATCH] Some basic conditionals

- No terminator analysis yet
---
 examples/conditions.e0         | 10 ++-------
 src/codegen/llvm_ir/expr.rs    | 20 ++++++++++++++---
 src/codegen/llvm_ir/if_else.rs | 41 ++++++++++++++++++++++++++++++----
 src/parser.lalrpop             |  2 +-
 4 files changed, 57 insertions(+), 16 deletions(-)

diff --git a/examples/conditions.e0 b/examples/conditions.e0
index 08cf616..67b4476 100644
--- a/examples/conditions.e0
+++ b/examples/conditions.e0
@@ -5,13 +5,7 @@ fn main() -> int {
     return 10;
   } else if x > 50 {
     return 50;
-  } else {
-    if x < 20 {
-      return 20;
-    } else if x > 40 {
-      return 40;
-    } else {
-      return x;
-    }
   }
+
+  return 65;
 }
diff --git a/src/codegen/llvm_ir/expr.rs b/src/codegen/llvm_ir/expr.rs
index 7b776f8..b3514a8 100644
--- a/src/codegen/llvm_ir/expr.rs
+++ b/src/codegen/llvm_ir/expr.rs
@@ -44,13 +44,27 @@ impl<W: Write> LlvmIrCodegen<W> {
           None => bail!("Invalid types on operation."),
         };
 
+        let common_ty = type_to_llvm(&left.ty);
         let left = self.convert_expr(left)?;
-
         let right = self.convert_expr(right)?;
 
         match op {
-          Op::LessThan => todo!(),
-          Op::GreaterThan => todo!(),
+          Op::LessThan => writeln!(
+            self.writer,
+            "{} = icmp slt {} {}, {}",
+            expr_ref,
+            common_ty,
+            left.as_str(),
+            right.as_str(),
+          )?,
+          Op::GreaterThan => writeln!(
+            self.writer,
+            "{} = icmp sgt {} {}, {}",
+            expr_ref,
+            common_ty,
+            left.as_str(),
+            right.as_str(),
+          )?,
           Op::Plus => writeln!(
             self.writer,
             "{} = add {} {}, {}",
diff --git a/src/codegen/llvm_ir/if_else.rs b/src/codegen/llvm_ir/if_else.rs
index 701e433..4599703 100644
--- a/src/codegen/llvm_ir/if_else.rs
+++ b/src/codegen/llvm_ir/if_else.rs
@@ -2,7 +2,7 @@ use std::io::Write;
 
 use anyhow::Result;
 
-use crate::ast::{IfElse, Stmt, Type};
+use crate::ast::{ElseClause, IfElse, Stmt, Type};
 
 use super::LlvmIrCodegen;
 
@@ -11,9 +11,42 @@ impl<W: Write> LlvmIrCodegen<W> {
     &mut self,
     if_else: &IfElse<Type>,
   ) -> Result<()> {
-    // Build condition
-    let cond = self.convert_expr(&if_else.cond);
+    // Use a common identifier so they have the same number
+    let cond = self.gensym(None, "cond");
+    let success_label = format!("{cond}.success");
+    let fail_label = format!("{cond}.fail");
+    let exit_label = format!("{cond}.exit");
 
-    todo!()
+    // Build condition
+    let cond = self.convert_expr(&if_else.cond)?;
+    writeln!(
+      self.writer,
+      "br i1 {}, label %{}, label %{}",
+      cond.as_str(),
+      success_label,
+      fail_label
+    )?;
+
+    // If true
+    writeln!(self.writer, "{}:", success_label)?;
+    self.convert_stmts(&if_else.body)?;
+    writeln!(self.writer, "br label %{}", exit_label)?;
+
+    // If false
+    writeln!(self.writer, "{}:", fail_label)?;
+    match &if_else.else_clause {
+      Some(ElseClause::If(if_else2)) => self.convert_if_else(if_else2)?,
+      Some(ElseClause::Body(body)) => self.convert_stmts(body)?,
+      None => {}
+    }
+    writeln!(self.writer, "br label %{}", exit_label)?;
+
+    // Exit branch
+    writeln!(self.writer, "{}:", exit_label)?;
+    // No-op in case this is the last statement
+    let nop = self.gensym(Some("%"), "nop");
+    writeln!(self.writer, "{nop} = add i1 0, 0")?;
+
+    Ok(())
   }
 }
diff --git a/src/parser.lalrpop b/src/parser.lalrpop
index a1db41b..5273b37 100644
--- a/src/parser.lalrpop
+++ b/src/parser.lalrpop
@@ -41,7 +41,7 @@ Expr: Expr<()> = {
   "(" <expr:Expr> ")" => expr,
 
   #[precedence(level = "0")]
-  r"[0-9]+" => Expr { kind: ExprKind::Int(<>.parse::<i64>().unwrap()), ty: () },
+  r"-?[0-9]+" => Expr { kind: ExprKind::Int(<>.parse::<i64>().unwrap()), ty: () },
 
   #[precedence(level = "0")]
   Ident => Expr { kind: ExprKind::Var(<>), ty: () },